Vapor phase oxidation of propylene and butylene in the presence of an arsenic phosphomolybdate catalyst



June 22, 1965 PROPYLENE CONVERTED 'MOLE L. C.-'FETTERLY ETAL VAPOR PHASEOXIDATION OF PROPYLENE AND BU'IYLENE IN THE PRESENCE OF AN ARSENICPHOSPHOMOLYBDATE CATALYST Filed 'April 24, 1961 A T I 1 a i T f a i o l2 a 4 e ARSENOUS OXIDE BY WEIGHT A= TOTAL PROPYLENE CONVERSION BPROPYLENE CONVERTED TO ACRYLlC AC lD C= PROPYLENE CONVERTED TO ACRYLICACID PLUS ACROLEI NE D= PROPYLENE CONVERTED TO 00+ CO T'HE'IERI A-Gtures acrylic acid, for example, readily decomposes.

nited States Patent 3,190,913. VAPGR PHASE OXIDATHON F PROPYLENE ANDBUTYLENE IN THE PRESENCE GE AN ARSENIC PHGSPHOMOLZBDATE LATALYST LloydC. Fetterly, Oakland, Kenneth F. Koetitz, Concord, and George W.Conklin, Oakland, Qalif assignors to Shell (lil Company, New York, N.Y.,a corporation of Delaware Filed Apr. 24, 1%], Ser. No. 165,031

' 5 Claims. (Cl. 260533) This invention relates to improvements in theproduction of alpha,beta-unsaturated oxygen-containing compoundscomprising aliphatic monocarboxylic acids. The invention relates, moreparticularly, to an improved process for the direct vapor phaseoxidative conversion of propylene and/or isobutylene to acrylic acidand/or methacrylic acid, respectively.

Alpha,beta-unsaturated aliphatic monocarboxylic acids, such as, forexample, acrylic acid and methacrylic acid, because of their highlyreactive nature, are valuable starting and intermediate materials in anumber of important fields of application. However, their very reactivenature also contributes materially to the problems heretofore generallyencountered in their large scale production. Processes disclosedheretofore directed to the production of acrylic and/ or methacrylicacid areoften based upon operational procedures which are not onlycomplex and relatively costly, but which, in addition, do not lendthemselves readily to efficient large scale operations. These compriseliquid phase operations which are often difficult to control andgenerally necessitate the use of relatively costly equipment.

A potential source of these alpha,beta-unsaturated acids is theircorresponding olefins. As a consequence of relatively low yields *and/or costly operational steps involved in processes availableheretofore,large scale production of the acids from such starting materials has notfound general acceptance.

Processes have been disclosed heretofore directed to the production ofunsaturated acids from alpha,beta-unsat urated aldehydes. Thisprocedure, however, necessitates the separation and recovery, generallyby relatively costly, complex operative procedures, of the initiallyproduced unsaturated aldehydes before their subsequent conversion to theunsaturated acids. Because of the extreme reactivity of theseunsaturated aldehydes and acids substantial conversion to undesiredby-products under conditions generally prevailing in vapor phaseoperations disclosed heretofore is generally encountered. At elevatedtempera- In the presence of most oxidation catalysts this tendency isgenerally increased so that in their presence, at conditions prescribedheretofore, the rate for reactions involving decomposition of acrylicacid approaches, and often. exceeds, that of its formation. 7

It is, therefore, an object of the present invention to provide animproved process enabling the more efiicient vapor phase, oxidativeconversion of normally gaseous olefinic hydrocarbons toalpha,beta-unsaturated oxygencontaining products comprisingalpha,beta-unsaturated monocarboxylic acids.

Another object of the present invention is the provision of an improvedprocess enabling the more efiicient single 3,19%,9l3 Patented June 22,I965 stage, vapor phase, oxidative conversion of normally gaseousolefinic hydrocarbons having from three to four carbon atoms to themolecule to alpha,beta-unsaturated oxidation products comprisingsubstantial amounts of alpha, beta-unsaturated aliphatic monocarboxylicacids corresponding to said normally gaseous hydrocarbons.

Still another object of the present invention is the provision of animproved process enabling the more efiicient production of acrylic andmethacrylic acids by vapor phase, catalytic oxidation of propylene andisobutylene, respectively.

One particular object of the present invention is the provision of animproved process enabling the more efficient single stage, direct, vaporphase, catalytic, oxidative conversion of normally gaseoushydrocarbonscomprising propylene to acrylic acid. Other objects and advantages ofthe present invention will become apparent from the following detailedd'escriptionthereof.

In accordance with the present invention normally gaseous olefinichydrocarbon-s such as, for example, propylene and isobutylene, areoxidatively converted to alpha,betaunsaturated oxidation productscomprising alpha,beta-unsaturated monocarboxy-lic acids such as, forexample, acrylic and methacrylic acid, respectively, by contacting saidhydrocarbons, in admixture with molecular oxygen, with a catalystconsisting essentially of phosphomolybdic acid in combination witharsenic.

The hydrocarbon charge to the process of the invention comprisesolefinically unsaturated hydrocarbons. The invention is applied withparticular advantage to normally gaseous hydyrocarbons comprisingpropylene and/or isobutylene. Propylene is converted to. acrylic acidandisobutylene to methacrylic acid under the conditions of the presentlyclaimed invention as defined herein. The olefins charged to the processneed not necessarily be in a pure state. They may comprise materialswhich are in the vapor state and which do not undergo any substantial reaction, and which do not adverselyatlect the desired olefin oxidationunder the conditions of the presently claimed process. A normallygaseous olefinic charge .may inelude, in addition to propylene and/ orisobutylene, normally gaseous paratfinic hydrocarbons, suchas, forexample, methane, ethane, propane, butanes, or other paraffins which arein the vapor state under the conditions at which the claimed process isexecuted. Particularly suitable charge materials comprise thecommercially available propyleneand isobutylene-containing hydrocarbonfractions. The inclusion of normally gaseous parafiinic hydrocarbon-sis, at times, advantageous. Such diluent materials function asentrainin'g agents for the reaction mixture and aid in maintaininguniformity of reaction conditions Within the respective reaction zones.w

In accordance with the process of the invention, the

' olefin-containing charge, in admixture with added oxygen oroxygen-containing gas, is passed through a catalystcontaining reactionzone. Oxygen charged as oxygen reaotant may consist of concentratedmolecular oxygen, such as obtained, for example, by the fractionation ofair, or it may consist of a more dilute molecular oxygen-containing gas.A suitable oxygen-containing gas comprises, for example, molecularoxygen in admixture with an inert diluent gas, such as, for example,nitrogen. Air may be used as the source of the molecular oxygenreactant. The oxygen-containing charge may be admixed with the 3olefinic charge to the system before its introduction into the reactionzone or it may be introduced in part, or in its entirety, directly intothe reaction zone. Oxygen and/ or olefinic charge may be introduced intothe reaction zone at one or a plurality of points thereof.

Within the reaction zone, the reactants are brought into contact with acatalyst consisting essentially of phosphomolybdic acid in combinationwith arsenic or a suitable compound of arsenic. The arsenic component ofthe catalyst combination is preferably present in combination withoxygen, for example, as an oxide and/or form and/ or salt of the acidform. The arsenic-modified phosphomolybdic acid catalysts employed inthe process of the invention may be prepared by physical admixture ofthe phosphornolybdic acid with one or more arsenic compounds. The may bemixed in the dry state and the resulting physical admixture used assuch; or use may be made of suitable carrying media in preparing thecombination. Thus, the phosphomolybdic acid or the arsenic component, orboth, may be dissolved or suspended in a suitable liquid medium and thencombined; the carrying medium being thereafter removed by suitable meanscomprising one or more such steps as, for example, decantation,evaporation, filtering, centrifuging, and the like. One or bothcomponents may be combined with a suitable carrying medium such as, forexample, water, or any other suitable inert liquid, to form a pastebefore being admixed with each other. The resulting mixture is thendried and calcined. Comprised within the scope of the invention is thepretreatment of the phosphomolybdic acid with arsenic or a compoundthereof under conditions resulting in the decomposition of the arseniccomponent and/ or the oxidation of arsenic etc., to result in a finalmixture comprising phosphomolybdic acid in combination with an oxide ofarsenic.

The arsenic content is maintained within the range of from about 0.1 toabout 10%, and preferablyy from about 0.1 to about 5% by weight(calculated as elementary arsenic) of the catalyst. Particularlypreferred are catalysts containing arsenic in the amount of from about0.5 to about 2% by weight of the catalyst, which range, it has beenfound, is definitely critical with respect to the obtaining of optimumand unexpected results. Thus, by reference to Example III hereinafterand to the attached drawing showing a correlation between arseniccontent of the catalyst and results obtained therewith, it is seen thatlittle if any acrylic acid is produced with an arsenic content in thecatalyst below about 0.1% (curve B) and that the greater part of thereaction products obtained consists of oxides of carbon (curve D). Ithas now been found that the by-product reactions leading to theformation of oxides of carbon are suppressed to a surprising degree byincorporating arsenic in the catalyst in an amount above about 0.1% w.,and that suppression of the oxides of carbon forming-reaction becomesprogressively more marked with increase in arsenic content until in thevery critical range of from about 0.5% to about 5% w. of arsenic in thecatalyst there is obtained a maximum production of desired acrylic acid(curve B) with substantially reduced oxides of carbon production (curveD). In general, it is found that the arsenic content of about 5% neednot be exceeded. Above this amount there is a definite trend toward adecrease in acrylic acid production with a simultaneous increase inacrolein formation, which, however, does not become very marked untilthe arsenic content is permitted to exceed about 10% w. of the catalyst.It is furthermore apparent from the attached drawing that the remainderof the products in a once through operation will consist predominentlyof acrolein (curve C) which valuable product is, upon recycling toextinction in a continuous operation, readily converted to additionacrylic acid.

A particularly preferred catalyst combination consists essentially ofphosphomolybdic acid in admixture with arsenous oxide. The catalyst maybe employed as such,

or in further combination with a suitable solid catalyst supportmaterial. A particularly preferred catalyst support material,particularly advantageous when employing phosphomolybdic acid incombination with arsenous oxide is silica. The silica support may becombined with the preformed phosphomolybdic acid-arsenous oxidecombination, or it may be combined with the catalyst combination duringits preparation. The silica may comprise, for example, from about 5% toabout 75%, and preferably from about 5% to about 10% by weight of thecatalyst. One method of preparing a suitable arsenicmodifiedphosphomolybdic acid catalyst is illustrated by the following example:

Example I To 134.5 grams of phosphomolybdic acid dissolved in .100 cc.of water there is added at 50 C. 320 grams of dry arsenous oxide (AS203)in powder form. To the resulting mixture there is added 42 g. ofstabilized silica sol (Ludox). A stream of hot air is then passedthrough the resulting mixture to evaporated water and convert themixture into the form of a paste. The resulting paste is dried in air,calcined 2 hours at 250 C. and another three hours at 500 C. Thecalcined product was screened to obtain a 10/20 mesh size. The resultingcatalyst consisted essentially of arsenous oxide-modifiedphosphomolybdic acid containing 1.5% by weight of arsenic acid, 8.4% byweight of silica.

Other methods of preparing suitable arsenic-modified phosphomolybdicacid catalysts comprise, for example: the treatment of phosphomolybdicacid at an elevated temperature, up to but not substantially above about450 C. with arsenic; the addition of aqueous ammoniacal AS203 to hotaqueous phosphomolybdic acid followed by drying and calcining of theresulting mixture, etc.

The phosphomolybdic acid component of the suitable catalysts maycomprise the commercially available phosphomolybdic acids. Suitablephosphomolybdic acids include phospho-12-molybdic acid and thephospho-18- molybdic acid. The phosphomolybdic acid component may beprepared by conventional means, for example, by reaction of molybdenumtrioxide or the sodium molybdenum trioxide with phosphoric acid.

Although a catalyst consisting essentially of arsenous oxide-modifiedphosphomolybdic acid in combination with silica has been chosen in theforegoing illustrative example it is to be understood that the inventionis in no wise limited to the use of only those arsenic-modifiedphosphomolybdic acid catalysts containing arsenic in the arsenous oxideform. The arsenic may be employed, for example in the form of an oxideof trivalent or pentavalent arsenic. Other specific examples of suitablearsenic components comprise arsenous acid, metallic arsenides such as,for example, Cu AS, FeAs CoAsetc., compounds of arsenic with halogensuch as AsCl AsCl AsBr Asl AsI AsI compounds of arsenic with sulfur suchas, for example, AS283, As S Fesz FGAS (arsenopyrite), etc.

Since the arsenic component may possess appreciable volatility under theconditions employed, depending upon the specific form in which arsenicis used, it is at times prepared to employ arsenic in combination withan agent reducing its volatility without adversely affecting to anysubstantial degree its effectiveness. Such agent may be present inphysical or chemical combination with the arsenic. Thus, a part or allof the arsenic component may be present as a metal salt of a metal, forexample, lead arsenate, tin arsenate, and other combinations of arsenicwith metals having little if any volatility under the conditions used.

The suitable catalysts employed in the process of the invention maycomprise the arsenic in more than one form. Thus, the arsenic may bepresent in the form of example, as arsenomolybdic acid. It is tobestressed however, that the requisite proportion of phosphomolybdicacid is present as such, regardless of the form in which the arsenic ispresent in the combination catalyst.

Although silica is indicated herein as a preferred A part or all of thearsenic compound may be 6 Pressures in the range of from aboutatmospheric to about 50 p.s.i.g. are generally satisfactory althoughsomewhat higher pressures, for example, up to about 150 catalyst supportmaterial, it is to be understood that the invention is not limited tosupported catalyst comprising this specific supported material. Thus, apart or all of the catalyst support employed may consist of one'or moreof such materials, for example, as the known aluminous supports, at theadsorptivev aluminas, bauxite, Porocel; combinations of silica andalumina; Alundum; aloxite; and other materials such as Carborundum,silicon, silicon carbide, ceramically bonded aluminous and/or siliciousmaterials, clays, fire brick, charcoals, activated carbons, etc.

Although the essential components of the catalysts used in theprocess ofthe present invention comprise phosphomolybdic acid and arsenic, othercomponents capable of modifying the catalyst may be present in' minoramounts. Such modifiers comprise, for example, one or more metals, suchas Fe, Cu, Pb, Cu, Ni, W, Pb and Sb or oxides thereof. 'Such modifiersmay be present in amounts not substantially exceeding about 1% by weightof the combination catalyst. The metal bismuth and compounds thereof,are avoided since they are found to e have an adverse eifect upon theacrylic acid production in the presence of the arsenic-modifiedphosphomolybdic acid catalysts.

The addition of arsenic, or a compound of arsenic, during the course ofthe process is contemplated within the scope of the invention. made incontrolled amounts to assure the maintenance of the arsenic within theabove-prescribed permissible amount within the system. The addition ofthe arsenic,

Such addition of arsenic is or compound thereof, during the course ofthe oxidation process may be carried out by introducing the arsenic inthe form of a vapor, mist, dust, smoke, or thelike, into the bed ofcatalyst in the reaction zone. The introduction of the arsenic into thereaction zone may furthermore be effected by dissolving, or suspending,the arsenic in a suitable solvent or carrying medium before introduction into the system. The process of the invention may be carried outwith the catalyst in the form of a solid fixed bed, as a suspension, oras a fluid catalyst bed. When using the catalyst in the form of asuspension, or as a fluid bed, make-up arsenic as required may be addedto the catalyst recycled within the system.

When, after prolonged use, the catalysts used in the process of theinvention have lost to some extent their desired activity, they may bereactivated by heating in an oxygen-containing stream'such as, forexample, air, which may be diluted with an inert gas, such as flue gasor the like, at elevated temperatures, for example, from about 500 toabout 600 C. The time of such heating may vary within the scope of theinvention. In general, a period of from about 0.5 to about 2 hours willbe found satisfactory. Longer or shorter heating times may, however, beused within the scope of the invention. After the heating step thecatalyst is treated with arsenic, or'an arsenic compound to assure thepresence of the arsenic in the regenerated catalyst in an amount withinthe abovedefined range. Regeneration of the catalyst may be carried outin situ.

Reaction of the olefinic charge with oxygen in accordance with theinvention is carried out at a temperature of from about 450 to about 600C. and preferably in the range of from about 475 to about 550 C. The useof a temperature in the range of from about 495 to about 525 C. isgenerally still more preferred. Somewhat higher or lower temperaturesmay, however, be employed within the scope of the invention.

p.s.i.g. may at times be advantageously employed. In general, it isfound that acrylic acid production rate is not improved by increase inpressure, and the use of the lower pressures is in general preferred.The use of atmospheric, subatmospheric or superatmospheric pressuresbroadly, is, however, comprised within the scope of the invention.v

Contact times preferably employed may vary considerably within the scopeof the invention in accordance with temperature and specific catalystused. In general, a contact time in the range of from about 0.1 to about10 seconds may be employed. Higher or lower contact times may, however,be used within the scope of the invention. Acrylic acid formation in thepresence of the. catalysts of the invention is generally favored byrelatively short contact times. The use of a contact time in the rangeof from about 0.1 to about 5, and preferably from about 0.5 to about 2seconds are usually employed.

The rate at which propylene and oxygen'are fed to the reaction zone ispreferably controlled to maintain a mol ratio of propylene to oxygen inthe feed in the range of "from about 110.15 to about 1:3, andpreferably. about 1:1 to 1.12. Higher or lower relative ratios of thesefeed components may, however, be employed within the scope of theinvention. In general, it is preferred to maintain a molecular excess ofoxygen over propylene in the feed to the process. Aparticularly'preferred ratio comprises a ratio of propylene to oxygen ofabout 111.5 when employing a catalyst consisting essentially of aphosphomolybdic acid-arsenous oxide-silica combination.

Water vapor is preferably added to the system. Care is however taken toassure that no substantial amount of liquid Water comes into contactwith the catalyst during the operation. The Water vapor may beintroduced into the reaction zone in a molar proportion of water topropylene of from about 1:1 to about 12:1, and preferably from about 3:1to about 8:1. Greater or lesser amounts of water vapor may, however, beintroduced into the system in accordance with the invention.

Diluents, such as normally gaseous materials or materials which areinvapor state under conditions of executionof the reaction, and whichare. relatively inert and do not undergo any substantial reaction duringthe course of the process, may be .introducedinto the system.Suitablediluents comprise, for example,.parafiinichydrocarbons,.fiue.gas, nitrogen,.etc. Suchdiluent fluids areoptionallyintroduced intothe .system to aid in maintaining desiredconditions of temperature and contact time. Addition of heat to, orwithdrawal of heat from such diluents before their introduction into thesystem may be resorted to within the scope of the invention.

Under the above-defined conditions olefins will react with molecularoxygen with the formation of reaction products comprising substantialamounts of the corresponding alpha,beta-unsaturated monocarboxylic acid.In addition thereto there are obtained substantial amounts of thecorresponding alpha,beta unsaturated aldehyde. Thus, when chargingpropylene the reaction products will consist essentially of acrylic acidand acrolein. When charging isobutylene the reaction products willconsist essentially of methacrylic acid in admixture with methtillation,fractionation, extractive distillation, scrubbing,

absorption, adsorption, liquid-liquid extraction, etc.

A particular advantage inherent in the process of the invention residesin the fact that the high production rate of alpha,beta-unsaturatedmonocarboxylic acid, in the presence of water vapor, now makes possiblethe separation of the reactor efiluent by simple indirect cooling,optionally with the aid of liquid quenching, for example, with water,into a normally liquid fraction comprising the greater part of theunsaurated acid product from a vapor fraction comprising the greaterpart of the unsaturated aldehydes produced. Thus, in the production ofacrylic acid from propylene, the reactor effiuence is subjected tocontrolled partial condensation to result in the separation of a liquidphase, comprising water and acrylic acid, from a vapor phase, comprisingacrolein and unconverted propylene. The acrolein content may beseparated from such gaseous phase and recovered as a final product ofthe process. In a preferred method of carrying out the process of theinvention, however, such vapor phase is recycled, at least in part tothe reaction Zone to effect the substantially complete conversion of therecycled acrolein to acrylic acid.

Acrylic acid is separated from the liquid phase, separated from thereactor eflluence by controlled cooling by conventional means, andrecovered as the essential final product of the process of theinvention.

In this wise propylene is oxidatively converted in continuous recycleoperation to acrylic acid efliciently with yields of 34% and higher. Thefollowing examples are illustrative of the presently claimed invention:

Example II Mol percent Tot-a1 propylene conversion 65.7 Propyleneconverted to:

Acrolein 24.1 Acrylic acid 15.7 Acetic acid 2.9 Acetaldehyde 0.6 Maleicacid 1.0 Acetone 0.7 Oxides of carbon 20.4

This represents a selectivity to acrolein of 36.7% and to acrylic acidof 23. 9% based on propylene,

The operation was repeated under substantially identical conditions butwith the exception that the reactor efiluence was subjected tocontrolled cooling to eifect partial condensation of the efiluent streamwith the formation of a liquid phase containing aqueous acrylic acid anda vapor phase containing unreacted propylene and acrolein. The vaporphase was recycled to the reaction zone with the exception of a smallportion which was bled from the system. In this wise there was obtaineda conversion of propylene to acrylic acid of 37.8%. This represents aselectivity to acrylic acid of 42% based on propylene reacted.

Example III In a plurality of operations a mixture of propylene, air andsteam, containing a mole ratio of propylene to oxygen to steam of1:1.5:6, respectively, was passed through a bed of arsenic-modifiedphosphomolybdic acid consisting of phosphomolybdic acid-arsenousoxide-silica, at a temperature of 514 C., a pressure of about 2 p.s.i.g.and with a Contact time of 0.5 Second. The catalysts used were preparedas described in the foregoing Example I and contained 8 9% by weight ofsilica. The rest of the catatent shown in the abscissa of the graph ofthe attached drawing. The plurality of operations were carried out undersubstantially identical conditions but with the exception that thearsenic content of the catalyst was varied. One run was made with aphosphomolybdic acid-silica catalyst containing 11% w, silica' but noarsenic component, under otherwise identical conditions as the otherruns. The products obtained in each of the operations were determined.The resultsobtained are indicated in the graph of the attached drawingwherein are plotted versus arsenous oxide content of the catalyst(abscissae): (1) total propylene conversion-Curve A, (2) propyleneconverted to acrylic acid Curve B, (3) propylene converted to acroleinand acrylic acidCurve C, and (4) propylene converted to carbon monoxideand carbon dioxideCurve D.

Example IV An arsenic-modified phosphomolybdic acid catalyst containingarsenic as lead arsenate was prepared by mixing 152 grams ofphosphomolybdic acid with 3 grams of lead arsenate and adding theresulting admixture to 50 grams of colloidal silica sol (circa 30% w.SiO The resulting mixture was dried and calcined for 4 hours at 500 C.The calcined mixture was broken and screened to 10/20 mesh size. Thecatalyst thus obtained consisted essentially of 88% w. ofphosphomolybdic acid, 9% w. silica and contained 0.31% w. arsenic in theform of lead arsenate.

A mixture containing propylene, air and water vapor, containing a molratio of C H :O :H 0 of 1:1.5 6, respectively, was passed over thecatalyst thus prepared at a temperature of 501 C., at a pressure of 3-4p.s.i.g., and a contact time of 0.5 second. A propylene conversion of64.6 was obtained with a selectivity to acrylic acid of 21.2% and toacrolein of 33.4%.

Similarly propylene was oxidized to oxidation products comprisingsubstantial amounts of acrylic acid with the use of a catalystconsisting essentially of phosphomolybdic acid, silica and tin arsenate.

Similarly methacrylic acid is produced by passing isobutylene inadmixture with air and steam over the aboveindicated arsenic-modifiedphosphomolybdic acid catalysts at the above-defined conditions.

We claim as our invention:

1. The process for the conversion of an olefin selected from the groupconsisting of propylene and isobutylene to a reaction mixture containingthe alpha,beta-unsaturated aliphatic aldehyde and alpha,beta-unsaturatedcarboxylic acid corresponding to said olefin, which consists essentiallyof reacting said olefin with uncombined molec ular oxygen, in vaporphase, at a temperature of from about 450 to about 600 C. in thepresence of a catalyst consisting essentially of arsenic-containingphosphomolybdic acid having an arsenic content of from about 0.1 toabout 10% by weight calculated as elementary arsenic.

2. The process in accordance with claim 1 wherein saidarsenic-containing phosphomolybdic acid consists essentially ofphosphomolybdic acid in combination with an oxide of arsenic, saidcombination containing from about 0.5% to about 5% by weight of arseniccalculated as elementary arsenic.

3. The process in accordance with claim 2 wherein said catalyst has anarsenic content of from about 0.5 to about 2% by weight calculated aselementary arsenic.

4. The process in accordance with claim 1 wherein said arsenic ispresent in said catalyst as arsenous oxide, and said catalyst is used incombination with an amount of silica in the range of from about 5 toabout by weight of said catalyst.

5. The process for the production of acrylic acid which consistsessentially of reacting propylene with uncombined molecular oxygen inthe presence of added steamand a References Cited by the Examinercatalyst consistingessent'ially of phosphomolybdic acid in UNITED STATESPATENTS combination with from about 0.1 to about 10% by weight v 1 p 260531 of arsenic, calculated as elementaryarsenic, at a tempera- 260:530ture of from about 450 to 600 C., thereby reacting pro- 5 2,941,007 6/60Callahan et aL pylene with uncombmed molecular oxygen with the forma- 3065 264 11/62 Koch et a1 260 533 tion of reaction products comprisingacrolein and acrylic acid, subjecting said reaction products to pantialconden- FOREIGN PATENTS sati-on, thereby separating a vapor phasecomprising acro- 903,034 8/62 Great Britain.

lein from a liquid phase comprising aqueous acrylic acid, 10 LORRAINE A.WELNBERGER Primary Exam-"en and recycling at least a pant of said vaporphase to said reaotiom LEON ZITVER, CHARLES B. PARKER, Examiners.

1. THE PROCESS FOR THE CONVERSION OF AN OLEFIN SELECTED FROM THE GROUPCONSISTING OF PROPYLENE AND ISOBUTYLENE TO A REACTION MIXTURE CONTAININGTHE ALPHA,BETA-UNSATURATED ALIPHATIC ALDEHYDE AND ALHPA,BETA-UNSATURATEDCARBOXYLIC ACID CORRESPONDING TO SAID OLEFIN, WHICH CONSISTS ESSENTIALLYOF REACTING SAID OLEFIN WITH UNCOMBINED MOLECULAR OXYGEN, IN VAPORPHASE, AT A TEMPERATURE OF FROM ABOUT 450 TO ABOUT 600*C. IN THEPRESENCE OF A CATALYST CONSISTING ESSENTIALLY OF ARSENIC-CONTAININGPHOSPHOMOLYBDIC ACID HAVING AN ARSENIC COONTENT OF FRO ABOUT 0.1 TOABOUT 10% BY WEIGHT CALCULATED AS ELEMENTARY ARSENIC.